fix: Mark tailwindcss as optional peer dependency

[amannn]

Mark tailwindcss as optional peer dependency

Description

When this plugin is included in a shareable config, the usage of Tailwind might be optional (see e.g. https://github.com/molindo/eslint-config-molindo).

Other popular ESLint plugin mark closely related peer dependencies as optional too for this reason (see e.g. eslint-plugin-jest

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

I know the strategy to be working from other ESLint plugins.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

[amannn]

@francoismassart Any chance this could be merged?